The present invention relates to cutting tools with cutting inserts and, more particularly, to cutting inserts having adjusted cutting edges.
Tools for machining operations such as milling, turning, boring, parting, grooving, threading, and drilling often include toolholders for holding one or more replaceable cutting inserts. The cutting inserts are typically made of a much harder material, such as cemented carbide, than the tool holder. The cutting inserts can be secured to the tool holder in any suitable manner, such as by brazing or, more typically today, clamping by means of a screw or a clamping arrangement.
Many cutting inserts have partially or completely elliptical or circular profiles and are used to cut a generally semi-circular or elliptical grooves in a workpiece. Other inserts have generally straight profiles and are designed to cut generally V-shaped, square, or rectangular grooves in a workpiece. For various reasons, such as to present a sharper cutting edge to a workpiece, inserts are often designed with a wedge angle at the cutting edges between the top and the side surfaces that is less than 90°. Also, the insert may be tilted so that a plane of the top surface is non-perpendicular to the workpiece, such as to present a cutting edge with a narrow wedge angle at a desired angle to the workpiece. Below the cutting edge, so that the side surface does not contact the workpiece after the cutting edge cuts into the workpiece, the side surface extends at a non-zero clearance angle to a plane of the top surface. Thus, an insert that has a generally circular profile when viewed along a perpendicular to a plane of the top surface may be generally frustoconical and have a smaller bottom surface than the top surface. An insert that is polygonal, such as triangular, square, rectangular, rhombic, etc, may also be smaller at the bottom surface than the top surface in order to provide a clearance angle.
It is also common for cutting edges to be designed to vary relative to a virtual plane of the top surface of the insert, e.g., the cutting edges may curve. This may be done to facilitate chip formation or removal, or for other reasons. While the curvature of the cutting edge may be desirable with respect to certain aspects of the machining operation, because of the non-zero clearance angle, the curve of the cutting edge alters the shape of the profile of the insert when viewed along a perpendicular to the plane of the top surface. This can result in a machined shape that is not desired. For example, it may not be possible to form a corner that has a desired radius or that is sufficiently square, or it may cause undesired ridges and grooves to be formed in a workpiece.
As seen in FIGS. 6A-6C and 7A-7C, showing generally circular inserts C25 and square edged inserts S25 for purposes of illustration, because the clearance surfaces C45 and S45 below the cutting edges C47 and S47 form a non-zero angle α with a perpendicular to the top plane CP and SP of the inserts, as the cutting edges move downward in the direction of the perpendicular to the top plane, the cutting edges recede from outermost points where the cutting edges are axially highest with respect to the perpendicular to the top plane. For example, as described in connection with the circular insert C25, the cutting edge C47 recedes from an outermost diameter DO where the cutting edge is highest to an innermost diameter DI where the cutting edge is lowest. The location of the cutting edge at DI differs from the location of the cutting edge at DO by a distance Δ. The diameter db of the bottom of the insert remains constant. The profiles of the cutting edges C47 and S47 when viewed in the direction of the perpendicular to the plane are not circular or square, which may be problematic. It is desirable to provide a cutting tool and an insert that can avoid such problems.
In accordance with an aspect of the present invention, a cutting insert comprises a virtual clearance surface that is one of substantially flat and planar and substantially frustoconical, the virtual clearance surface forming a non-zero angle with a perpendicular to a virtual plane of a top surface of the insert and a first virtual cutting edge disposed above the virtual clearance surface, all points on the first virtual cutting edge being disposed at the plane of the top surface. The cutting insert also comprises an adjusted clearance surface differing from the virtual clearance surface and forming the non-zero angle with the perpendicular to the plane of the top surface, and an adjusted cutting edge above the adjusted clearance surface, at least some but fewer than all points on the adjusted cutting edge being disposed at different distances from the plane of the top surface, a profile of the adjusted cutting edge viewed in the direction of the perpendicular to the plane of the top surface corresponding to a profile of the first virtual cutting edge.
In accordance with another aspect of the present invention, a cutting tool comprises a cutting insert comprising a virtual clearance surface that is one of substantially flat and planar and substantially frustoconical, the virtual clearance surface forming a non-zero angle with a perpendicular to a virtual plane of a top surface of the insert, a first virtual cutting edge disposed above the virtual clearance surface, all points on the first virtual cutting edge being disposed at the plane of the top surface. The cutting insert also comprises an adjusted clearance surface differing from the virtual clearance surface and forming the non-zero angle with the perpendicular to the plane of the top surface, and an adjusted cutting edge above the adjusted clearance surface, at least some but fewer than all points on the adjusted cutting edge being disposed at different distances from the plane of the top surface, a profile of the adjusted cutting edge viewed in the direction of the perpendicular to the plane of the top surface corresponding to a profile of the first virtual cutting edge. The cutting tool also comprises a tool holder comprising a recess for receiving the insert and at least one abutment surface for abutting at least one side insert supporting surface on the insert.